State of the art in cytogenetics, insights into chromosome number evolution, and new C-value reports for the fern family Gleicheniaceae.

Lucas Vieira Lima,Thaís Elias Almeida,Saulo Marçal De Sousa,Alexandre Salino

doi:10.1590/0001-3765202120201881

Abstract

Studies concerning the cytogenetics of Gleicheniaceae have been scarce, especially those employing evolutionary approaches. Two chromosome number evolutionary models have been hypothesized for Gleicheniaceae. One proposes that ancestral haploid numbers were small and that the chromosome numbers of extant species evolved through polyploidy. The other model proposes that, at the genus level, fern chromosome evolution occurred from ancestors with essentially the same high chromosome numbers seen in living lineages. Neither of those hypotheses has been tested based on phylogenetic frameworks. We sought to (i) present the state of the art of Gleicheniaceae chromosome numbers; (ii) test the two evolutionary models of chromosome numbers within a phylogenetic framework; (iii) test correlations between DNA contents and chromosome numbers in the family. We report here DNA C-values for five species, which increases the number of investigated taxa nearly twofold and report two new genera records. Ancestral state chromosome reconstruction corroborates the hypothesis that ancestral chromosome numbers in Gleicheniaceae were as high as those of extant lineages. Our results demonstrate the possible role of dysploidy in the evolutionary chromosome history of Gleicheniaceae at the genus level and suggest that the relationship between chromosome number and DNA content does not appear to be linear.

Highlights

IntroductionFerns and lycophytes stand out among vascular plants for their distinct genomic evolutionary histories, with the conservation of high chromosome numbers in taxa with diploid gene expressions (Haufler 1987, 2002, 2014)
Ferns and lycophytes stand out among vascular plants for their distinct genomic evolutionary histories, with the conservation of high chromosome numbers in taxa with diploid gene expressions (Haufler 1987, 2002, 2014). Evidence shows that those plants underwent multiple cycles of polyploidy (1KP 2019, Huang et al 2020), with subsequent diploidization involving gene silencing, but without apparent chromosome losses, so that high chromosome numbers were retained (Haufler 2002, 2014)
Whole Genome Duplication played a major role in fern and lycophyte speciation (Wood et al 2009) and influenced chromosome numbers and genome sizes (e.g., Klekowski & Baker 1966, Leitch & Leitch 2012, 2013, Barker 2013, Henry et al 2015)

Summary

Introduction

Ferns and lycophytes stand out among vascular plants for their distinct genomic evolutionary histories, with the conservation of high chromosome numbers in taxa with diploid gene expressions (Haufler 1987, 2002, 2014). A few fern lineages show exceptionally large (or very small) genomes, ferns are typically characterized by mediumsized genomes They are distinctive as compared to other land plants, as the only group with a correlation between genome size and chromosome numbers (Nakazato et al 2008, Clark et al 2016)

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